The present invention relates to a digital-mobile-wireless-communications apparatus and the system using the same.
In a zone-configured digital-mobile-wireless-phone system, a radio-wave-transmission environment changes every moment caused by a multipath fading. To deal with this problem, a transmission quality has been maintained by changing a zone or a transmission channel as needed while a telephone call is in progress. As the changes of the radio-wave-transmission environment of transmission paths highly depend on the velocity of a mobile phone, the velocity is calculated prior to a changeover, then the changeover is done based on the calculated velocity. For example, in Laid-open Japanese patent H998465, signals transmitted from a plurality of Global Positioning System (GPS) satellites are received by GPS-receiving antenna 901 of mobile phone 900 shown in FIG. 9. The received signal is led into radio-frequency-receiving circuit 902 to demodulate, then fed into GPS-signal-processing circuit 903. Circuit 903 decodes information on GPS-satellite""s orbital position and time information from the demodulated signal to output them to data-processing circuit 904. Circuit 904 calculates the current position of mobile phone 900 accurately, and the result is entered to velocity-detecting circuit 905. Circuit 905 calculates the velocity of mobile phone 900 based on the current-position information obtained at intervals over time, and outputs the calculated velocity to control circuit 909. Control circuit 909 sends a control signal, which is determined according to the magnitude of the velocity, to transmitting and receiving circuit 907, and changes a time period that monitors a transmission channel adjacent to the in-use channel (this time period is hereafter referred to as a monitoring period). If a channel whose radio-wave-transmission environment is better than that of the in-use channel is detected, control circuit 909 changes the transmission channel into the detected channel.
In such a conventional way, however, the accurately calculated velocity of a mobile phone has not been exploited fully. This velocity has been previously used for the purpose of changing the monitoring period of the adjacent channel. Specifically, because the detected velocity is not directly related to a physical measure representing a radio-wave-transmission environment of transmission paths, evaluating information on the radio-wave-transmission environment could not be obtained accurately. For example, the calculated velocity of a mobile phone is not related to a degradation of a bit-error-rate (BER), which is caused by a Doppler shift (Doppler frequency) of carrier frequencies for the mobile phone moving at a high speed. Although the way mentioned above is effective at finding a transmission channel having a good-conditioned transmission environment, another problem to be improved lies in the conventional way: the calculated velocity of a mobile phone is not related to a receiving-electric-field intensity of the mobile phone. That is, even if the mobile phone is moving at a high speed under the condition with a sufficient receiving-electric-field intensity, in other words, the condition with a favorable radio-wave-transmission environment, a changeover of the monitoring period is unnecessarily performed as is the case that the radio-wave-transmission environment is in a poor condition. Consequently, the transmission is often subjected to a momentary interruption.
By making efficient use of information on the velocity and the receiving-electric-field intensity of a mobile phone, it is possible to evaluate the radio-wave-transmission environment with much accuracy. The present invention thus enables to provide a digital-mobile-wireless-communications apparatus with a capability of getting a higher transmission quality.
The communications apparatus of the present invention operates at a receiver as follows:
1) Receiving velocity information for the communications apparatus, a velocity-signal generator converts the velocity information into an electric signal (hereafter referred to as a velocity signal.)
2) Receiving the velocity signal, a Doppler-frequency calculator calculates a Doppler frequency of a radio-wave corresponding to the velocity signal, then converts the Doppler frequency into an electric signal (hereafter referred to as a Doppler-frequency signal.)
3) Detecting a receiving-electric-field intensity at the input section of the communications apparatus, a receiving-electric-field-intensity-signal generator outputs the receiving-electric-field intensity as an electric signal (hereafter referred to as a receiving-electric-field-intensity signal.)
4) Receiving the two signals described above, i.e., the Doppler-frequency signal and the receiving-electric-field-intensity signal as input signals, transmission-environment-inference means evaluates the radio-wave-transmission environment of the communications apparatus based on the entered two signals, then outputs the result as an electric signal (hereafter referred to as a transmission-environment-inference signal.)
For a mobile-wireless-communications apparatus used in a digital communications system, it is generally known that the higher the velocity, the greater the Doppler shift affecting carrier frequencies. This degrades a bit-error-rate (BER), that is, it degrades the transmission quality. The relation between a shift of the carrier frequencies and the influence on the BER by the shift depends on which digital-modulation scheme is used, and the relation is often explained theoretically or experimentally under a radio-wave-transmission environment chosen as a model. Therefore, if the Doppler frequency under a modulation scheme can be calculated, the xe2x80x9cmost probablexe2x80x9d BER corresponding to the Doppler frequency can be also determined by applying data obtained from a radio-wave-transmission environment modeled after a real-world situation. In a like manner, the relation between the receiving-electric-field intensity and its influence on the BER also depends on which digital-modulation scheme is used, and the relation is often explained theoretically or experimentally under a radio-wave-transmission environment chosen as a model. Therefore, if the receiving-electric-field intensity under a modulation scheme can be calculated, the xe2x80x9cmost probablexe2x80x9d BER corresponding to the receiving-electric-field intensity can be also determined by applying data obtained from a radio-wave-transmission environment modeled after a real-world situation. Here, the xe2x80x9cmost probablexe2x80x9d has an implication that the modeled-radio-wave-transmission environment from which the data is obtained is not always fit to the actual radio-wave-transmission environment, in the both cases of the evaluations of the Doppler frequency and the receiving-electric-field intensity.
Therefore, calculating two physical measures, i.e., the Doppler frequency and the receiving-electric-field intensity, the communications apparatus of the present invention can estimate the radio-wave-transmission environment for transmission paths more accurate than before.
Some possible applications for the present invention are described below.
a) The velocity information fed into the velocity-signal generator may include information on a velocity itself of a vehicle or an airplane, or on the satellite position and time information transmitted from GPS satellites.
b) The receiving-electric-field-intensity-signal generator can generate a receiving-electric-field-intensity signal based on an output signal from a Received Signal Strength Indicator (RSSI). The RSSI is arranged to acquire d. c. voltage being proportional to a receiving-electric-field intensity of a received radio wave.
c) Transmission-environment-inference means can be arranged so as to output a transmission-environment-inference signal according to data obtained from a radio-wave-transmission environment model similar to the actual situation under a digital modulation scheme. The data mentioned above is based on a BER vs. receiving-electric-field-intensity characteristics, where the Doppler frequency is used as a parameter.
d) In communications between the communications apparatus and a plurality of base stations in zone-configured mobile communications system, the communications apparatus can change the base station to another to maintain a higher transmission quality, if the radio-wave-transmission environment of the transmission paths currently used is not in a good condition as a consequence of evaluating a signal transmitted from a communications partner.
e) The communications apparatus can provide a communications partner with a transmission-environment-inference signal, by which the communications partner can take measures for getting an improved transmission quality. For example, the communications partner can change a modulation scheme based on the obtained transmission-environment-inference signal.
f) In order to improve the transmission quality and speed, the communications apparatus can change an assigned number of spreading signals if necessary, when the communications apparatus uses a spectrum-spreading communications system.
g) In order to improve the transmission quality, the communications apparatus can adjust a transmitting power level to be an optimal condition, based on the transmission-environment-inference signal transmitted from the communications partner.
According to the present invention, as described above, the Doppler frequency and the receiving-electric-field intensity of the carrier frequencies for the communications apparatus are computed as two physical measures in the apparatus. In consequence of evaluating a relation between these two information items, i.e., the Doppler frequency and the receiving-electric-field intensity and the corresponded BER which has already been obtained from a transmission-environment model similar to an actual situation, a most probable radio-wave-transmission environment of the transmission paths is output. With the output signal, the communications apparatus can:
a) change the base station as a communications partner to another;
b) increase a transmission power;
c) change the modulation scheme of the communications by noting the output signal to the communications partner;
d) change an assigned number of spreading signals per user when the spectrum-spreading-communications system is used.
In this manner, the present invention enables to provide the communications apparatus with a capability of acquiring a higher transmission quality.